\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\begin{document}
\small
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    \draw[->] (0,-1)--(0,-2)node [below]{$G$};
    \draw[->] (-135:1)--+(0,-1)node [below]{$G$};
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    \draw[->] (45:1)--+(0,-.8)node [right]{$G$};
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  \begin{scope}[xshift=6cm]
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\end{tikzpicture}
\end{document}